Desulfurization of petroleum products with alkali metal followed by aqueous formaldehyde



r 2,748,058 Ice Patented May 29, 1956 DESULFURIZATION OF PETROLEUM PRODUCTS WITH ALKALI METAL FOLLOWED BY AQUE- OUS FORMALDEHYDE Joseph Frederic Walker, Lewiston, N. Y., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Application July 29, 1953, Serial No. 371,165

7 Claims. (Cl. 196-26) This invention relates to the purification of petroleum hydrocarbons and more particularly to the desulfurization of liquid petroleum products.

The presence of sulfur compounds such as mercaptans, heterocyclic compounds containing sulfur in the ring, organic sulfides, thioketones and sulfo acids in liquid petroleum products such as oils and gasoline, is quite objectionable and many desulfurization methods have been proposed. Petroleum crudes from the West Texas, Mexican, Venezuelan and Middle East oil fields are notoriously high in such sulfur compounds, as are also the liquid petroleum products produced therefrom. Removal of sulfur, present as sulfur compounds, from such products is generally regarded as essential since they poison hydrogenation catalysts usedin further processing operations, e. g. in reforming and platforming methods. Sulfur also decreases the lead susceptibility of gasoline and is objectionable in fuel fractions for diesel use. A large use of heavy fuel oils is in the firing of open hearth furnaces in the steel industry where a high sulfur content of the fuel is especially undesirable.

It has been proposed to remove sulfur from such products by treatment with metallic sodium, e. g. by agitating the product at an elevated temperature with a dispersion of sodium, then decomposing residual sodium with steam or water. The sodium decomposes the sulfur compounds present to give sodium sulfide, sodium mercaptides and unsaturated hydrocarbon by-products, a portion of which are polymerized by the sodium. On treatment with steam or water to destroy unreacted sodium and remove reaction products, some of the resulting sulfur compounds dissolve in and are removed by the water, while others remain dissolved in the oil phase. Some of the highly unsaturated hydrocarbons also remain in the oil and cause trouble. Thus, such a treatment with sodium has not been as satisfactory as desired since it converts original sulfur compounds to other sulfur compounds and to unsaturated hydrocarbons, both of which are retained in objectionable amounts by the oil. Another objectionable feature of such a treatment is the relatively large amount of sodium required for effective treatment.

It is an object of the present invention to provide an improved method for removing sulfur compounds from liquid petroleum products. A further object is to provide a method for removing sulfur compounds from such products involving the treatment thereof with metallic sodium, followed by a treatment with formaldehyde. Still further objects will be apparent from the following description.

The above objects are accomplished in accordance with the invention by subjecting a petroleum product which contains objectionable amounts of sulfur impurities such as mercaptans and other sulfur compounds, in the liquid phase to the action of an alkali metal at an elevated temperature, and then subjecting the resulting product to the action of an aqueous solution of formaldehyde.

It has now been found that metallic sodium converts the original sulfur impurities into sulfur compounds which can be effectively removed from the hydrocarbon phase by treatment with formaldehyde. The intermediate sulfur compounds appear to be converted by the formaldehyde into products which are either water-soluble or oil-insoluble so that they are readily removed from the oil by simply leaching the treated oil with a dilute aqueous formaldehyde solution. The treatment with formaldehyde can follow directly the sodium treatment, or it can be preceded by an intermediate treatment with steam or water, e. g. water extraction, by an intermediate filtration, or by combinations of such treatments. It has been found that the present formaldehyde treatment is effective to reduce the sulfur content about 30 to 60% below the value resulting from a treatment with sodium alone. An additional advantage resulting from the subsequent formaldehyde treatment is that formaldehyde reacts with unsaturated gum formers produced during the sodium treatment to give products of low volatility. The combined treatment permits obtaining a given reduction in sulfur content using substantially less sodium than when sodium alone is used.

The invention is illustrated by the following examples in which all percentages stated are percentages by weight.

Example 1 A heavy (No. 6) fuel oil fraction derived from a sour West Texas crude and containing sulfur compound impurities was treated with metallic sodium in a round bottom glass flask equipped with a mechanical stirrer, a reflux condenser, a nitrogen bleed and a heating bath. The oil was charged to the flask and then heated to and maintained at a temperature of 204 C. by suitably heating the surrounding bath. The oil was maintained under a nitrogen atmosphere during the entire heating period. When the oil had reached the temperature indicated, a dispersion of sodium in deobase kerosene containing 50% sodium was added to the oil in an amount corresponding to 6.1% sodium based on the weight of the oil. This amount of sodium was equivalent to 4.18 atoms of sodium per atom of sulfur (present as sulfur compounds) in the oil. About of the sodium particles in the dispersion added were less than 10 microns in diameter. The resulting mixture was maintained at about 204 C. for 2 hours while the stirrer was operated at about 860 R. P. M.

The mixture obtained from the above procedure was added to 5 volumes (per volume of the mixture) of approximately 5% aqueous formaldehyde which had been heated to 8090 C. During this addition, an inert atmosphere was maintained as a precaution against fires resulting from reaction of unreacted sodium and water. The quantity of formaldehyde employed was equivalent to 3 mols of CHzO per atom of sodium used in the original treatment. The resultant mixture was agitated for 20 minutes while maintaining the temperature at 8090 C. Approximately 12 volumes of cold water were then added and the mixture acidified with concentrated hydrochloric acid using methyl orange as an indicator. The resultant mixture, whose pH was not greater than 3, was then heated with agitation for about '15 minutes. The oil layer was decanted and heated in an inert atmosphere to remove water. Heating was continued until the vapor temperature exceeded about C.

The final sulfur content of the oil treated in the above manner was 0.39% as compared with 2.00% for the original oil. The sulfur content of a portion of the oil which had been simply extracted with water following the sodium treatment but had not been treated with formaldehyde was 0.95%.

Example 2 The procedure of the above example was repeated except that the sodium treatment was effected at 248 C. using an amount of the sodium dispersion equal to 3% of sodium based on the Weight of the oil. The sulfur content of the oil after treatment with both sodium and formaldehyde was 0.89% against an original value of 2.00%. The portion of the oil which was treated with sodium and extracted with water but was not treated with formaldehyde had a sulfur content of 1.29%. The combined sodium-formaldehyde treatments were carried out with an oil recovery of 98%.

The sulfur values reported above were determined by the Parr peroxide bomb method (Parr, The Analysis of Fuel, Gas, Water and Lubricants, 4th edition, 2nd impression, McGrawlill Book Company, p. 256 ff. (1932) As in previous sodium treating proposals, the sodium treatment should be carried out at an elevated temperature, the particular temperature used depending somewhat upon the petroleum product being treated and its sulfur content, the amount of sodium used and the degree of purification desired. In most instances, it will be preferable to employ a temperature of at least 200 C., e. g. 200 to 275 C., but higher temperatures up to just below the decomposition temperature of the product being treated can be used. The amount of sodium used will be governed largely by the degree of purification desired, considering, of course, the amount of impurities present in the product which is to be treated. For most purposes, an amount of sodium equal to from 1 to 5 atoms of sodium per atom of sulfur (present as sulfur compounds) in the petroleum product will give good results and it is preferred to continue the sodium treatment until reaction of the sodium is substantially complete. A large excess of sodium can be used if desired. The pressure during the sodium treatment should be sutficient to maintain the petroleum product in a liquid state, otherwise pressure is not an important factor. The use of an inert atmosphere, e. g. nitrogen, during the sodium treatment is preferred.

The formaldehyde treatment is preferably effected using a dilute aqueous formaldehyde solution, e. g. one containing 2 to Cl-IzO. More concentrated solutions, e. g. up to 37%, can be used but offer no added advantages. Instead of using preformed formaldehyde solutions, formaldehyde gas or paraformaldehyde can be added directly to the sodium treated product and the resulting product then extracted or leached with water. The amount of formaldehyde used can be varied considerably but ordinarily it will be advantageous to employ at least 1 mole, e. g. l to 5 moles and preferably 2 to 3 moles of CHzO per atom of sodium used in the first treatment. Much larger amounts of formaldehyde can be used but are not recommended for economic reasons. Any temperature up to the boiling point of the formaldehyde solution can be used but temperatures within the range 25 to 90 C. are generally preferred.

The formaldehyde treatment is effective under alkaline, neutral or acidic conditions. When the formaldehyde is added directly to the sodium-treated product, alkaline conditions will prevail. If desired, the aqueous formaldehyde can be added and used under distinctly acidic conditions, but no advantage derives from the use of acidities greater than about pH 2. Indications are that acidities higher than about pH 2 are not desirable in that they tend to convert sulfur reaction products into oil-soluble compounds, thus tending to hinder removal of sulfur.

While the invention has been described with specific reference to the use of sodium, it is to be understood that any other alkali metal such as potassium or lithium, or any alloy of such metals, e. g. sodium-potassium alloys, can be used in place of sodium with substantially the same results, and that the use of such other alkali metals or alloys thereof are within the scope of the invention.

The method of the invention is particularly well suited to the treatment of petroleum oils such as heavy fuel oils, as illustrated in the examples. It is, however, effectively applicable to any sulfur-containing petroleum product, including kerosene and gasoline fractions, which is or can be maintained in the liquid state under the conditions used in the treatments.

I claim:

1. The method of treating a petroleum product containing an objectionable amount of sulfur compound impurities comprising treating said product in the liquid phase at an elevated temperature with an alkali metal and subsequently treating said product with an aqueous solution of formaldehyde.

2. The method of claim 1 wherein the petroleum product treated is a fuel oil.

3. The method of claim 1 wherein sodium is the alkali metal used.

4. The method of claim 1 wherein the treatment with an alkali metal is effected at a temperature of at least 200 C. but below the decomposition temperature of the petroleum product.

5. The method of treating a petroleum product containing an objectionable amount of sulfur compound impurities comprising treating said product in the liquid phase at a temperature of at least 200 C. but below the decomposition temperature of said product with metallic sodium in an amount equal to 1 to 5 atoms of sodium per atom of sulfur present as sulfur compound impurities, said treatment being continued until reaction of the sodium has been substantially completed, then treating the resulting product with an aqueous solution of formaldehyde whose formaldehyde content corresponds to 1 to 5 moles of CHaO per atom of sodium used.

6. The method of claim 5 wherein the aqueous formaldehyde solution has a pH greater than 2.

7. The method of claim 5 wherein the sodium treatment is carried out at 200-275 C.

References Cited in the file of this patent UNITED STATES PATENTS 1,938,670 Sullivan et a1 Dec. 13, 1933 2,058,131 Carlisle Oct. 20, 1936 2,567,174 Anmdale et al. Sept. 11, 1951 2,614,966 Vanderbilt Oct. 21, 1952 FOREIGN PATENTS 213,661 Great Britain Apr. 2, 1924 

1. THE METHOD OF TREATING A PETROLEUM PRODUCT CONTAINING AN OBJECTIONABLE OF SULFUR COMPOUND IMPURITIES COMPRISING TREATING SAID PRODUCT IN THE LIQUID PHASE AT AN ELEVATED TEMPERATURE WITH AN ALKALI METAL AND SUBSEQUENTLY TREATING SAID PRODUCT WITH AN AQUEOUS SOLUTION OF FORMALDEHYDE. 